Masking effect?

hi, does anyone know how the effect in this site was done: http://www.motion-wave.com/
i really like the effect ib the “work” section where the photo comes in like windowblinds/shutters are opening…any ideas how to do it.? i tried using a mask and separate gradient changing movie clips within it, but it doesnt seem to do the same thing at all… thanks :yoshi: